An image sensor accumulates electric charge at a different timing on a surface basis or on a line basis. In general, a system of matching the timings to accumulate electric charge on a surface basis is referred to as a global shutter system, and a system of matching the timings to accumulate electric charge on a line basis is referred to as a rolling shutter system. In the image sensors, a CCD image sensor employing the global shutter system has prevailed in the past, but a CMOS image sensor has recently attracted attention, the CMOS image sensor having less power consumption than the CCD image sensor and capable of being produced with a small number of parts and at low cost. This CMOS image sensor often employs the rolling shutter system in terms of structural issues. In both of the systems, when imaging is performed with a light source repeatedly blinking, due to a difference in electric charge accumulation timings of sensors, a light-dark difference (surface flicker) on the entire surface or a light-dark difference for each of lines (line flicker) appears.
For a flicker correction technique, there is known a method of adding and averaging video signals of M sequential frames to thereby obtain a flicker-corrected image (see Patent Literature 1). In this Patent Literature 1, the frame rate is divided by a light-source frequency (power-supply frequency×2), a resultant value is rounded, and a resultant integer is set as the number of frames as addition targets, M. Thus, those M frames are added and averaged.